(Cyclo)condensation of isocyanate compounds

ABSTRACT

The invention concerns the use of a compound comprising a nitrogenous heterocyclic group with five cyclic members including, at least two nitrogen atoms, one of the nitrogen atoms bearing a hydrogen atom to promote the opening/closing reaction of uretidione cycles in the presence of a nucleophile compound provided that, when the nitrogenous heterocyclic group is imidazole, the opening/closing reaction is not the closing reaction of the uretidione cycle in the presence of a quaternary ammonium salt.

[0001] The invention relates to a process intended for the opening ofuretidione rings or the closing of isocyanate compounds to uretidionerings.

[0002] A subject matter of the invention is more particularly the(cyclo)condensation of isocyanate compounds.

[0003] In the chemistry of polyisocyanates, in particular in processesfor the synthesis of polyisocyanate trimers having an isocyanurate ring,it is generally desirable, in particular for reasons of viscosity, toobtain a reaction product having a certain content of compoundscomprising a uretidione ring.

[0004] Generally, compounds comprising a uretidione ring, also known asdimers, are obtained by dimerization of isocyanate compounds in thepresence of a dimerization catalyst, such as a trialkyphosphine, atris(N,N-dialkyl)phosphotriamide or an N,N,N′,N′-tetraalkylguanidine.

[0005] In addition, WO 99/23128 discloses a process for the catalytictrimerization of isocyanate using a catalyst based on a quaternaryammonium salt in which imidazole or one of its derivatives is used ascocatalyst, so as to increase the reactivity of isocyanates, inparticular of cycloaliphatic isocyanates, and to efficiently control thereactivity, without depending on the content of hydrolyzable chlorinepresent in the starting isocyanate monomer.

[0006] Furthermore, the document discloses that the use of imidazole ascocatalyst of a trimerization reaction in which the catalyst is aquaternary ammonium salt results in the formation of dimeric compoundscomprising a uretidione ring.

[0007] The amount of imidazole or its derivatives is such that theimidazole/quaternary ammonium molar ratio is of about 14 or more.

[0008] Furthermore, it is known that imidazole and other nitrogenouscyclic compounds having a 5-membered nitrogenous heterocyclic groupcomprising at least two nitrogen atoms add to the isocyanate functionalgroup at ambient temperature in accordance with the reaction scheme:

[0009] R being the residue of an isocyanate compound after removal of anisocyanate functional group and HET-H being a nitrogenous heterocycliccompound as defined above, bonded to the NCO group via the NH group ofthe heterocycle.

[0010] At high temperatures, of about 80 to 100° C., the nitrogenousheterocycles as described above are released from the NCO functionalgroup according to the reaction scheme:

[0011] The release temperature of the nitrogenous heterocyclic compoundsis relatively low in comparison with other agents which block the NCOfunctional group. For this reason, imidazole and the nitrogenousheterocycles as defined above are regarded as “good leaving groups”.

[0012] Furthermore, it is known that, when the HET-H/NCO ratio is small,the equilibrium of the reaction is shifted toward the formation of theprotected form of the isocyanate (I).

[0013] The studies carried out by the inventors have allowed it to befound that, in the presence of an anionic compound, in particularresulting from a strong base, such as a cyclocondensation catalyst ofanionic nature, the reaction of an isocyanate with a heterocycle asdefined above surprisingly promotes the formation of a monouretidionecompound, also denoted by “true dimer”, resulting from thepolycondensation of two starting isocyanate molecules and comprising asingle uretidione ring.

[0014] The mechanism proposed by the inventors is based on thehypothesis that, in the presence of isocyanate and of an anioniccompound, as defined above, the 5-membered heterocyclic compoundpromotes the addition of the isocyanate functional group to the urea-HET(I) to give a biuret-HET compound, also denoted by “pseudobiuret”, offormula (II):

[0015] Because of the nucleofuge characteristics of the HET group, thispseudobiuret rapidly cyclodimerizes to “true dimer” with release ofHET-H, which rapidly reacts with the excess isocyanate functional groupsin accordance with the reaction scheme:

[0016] Everything happens as though the base composed of the anionicgroup of the cyclocondensation catalyst accelerated thecyclodimerization kinetics by promoting the abstraction of a proton fromthe pseuodbiuret, followed by a cyclization reaction of the nucleophilicnitrogen atom thus created onto the carbonyl group of the ureafunctional group with release of the vicinal HET heterocyclic group.

[0017] Regarding the heterocyclic groups comprising an NH group, theaddition of the nitrogenous heterocyclic group to the isocyanatefunctional group takes place via this group, with subsequent release ofa HET-H compound.

[0018] Regarding the substituted heterocyclic groups, the addition ofthe nitrogenous heterocycle probably takes place via an=N-functionalgroup of the nitrogenous heterocyclic compound.

[0019] In other words, in a reaction medium comprising isocyanate anduretidione functional groups, the kinetics of addition of a HET-H groupto the isocyanate functional group are faster than the kinetics ofaddition of HET-H to the “true dimer” compound.

[0020] Furthermore, the studies of the inventors have made it possibleto find that, when the level of NCO functional groups present in thereaction medium decreased and at a temperature of at least 40° C., theHET-H compound acted by opening the uretidione ring and promoted, in thepresence of an isocyanate monomer, the formation of a higher homologouscyclocondensation compound, in other words the cyclotrimerizationreaction.

[0021] It was moreover known that some nucleophilic compounds Nu—H couldpromote the opening of the uretidione rings to form the correspondingaddition products, according to the reaction scheme:

[0022] Thus, it is described in Houben-Weyl, “Methoden der OrganischenChemie”, 4th Edition, Georg Thieme Verlag (1983), pp 1110, thataliphatic amines open the uretidione ring at ambient temperature. On theother hand, alcohols open uretidione rings only at high temperature,generally from 140-150° C.

[0023] Surprisingly, the present invention has made it possible todetermine that the heterocyclic compounds defined above catalyzed theaddition reaction of nucleophilic compounds with the uretidione ring.

[0024] Thus, the in the case in particular of alcohols, the additionreaction of the alcohol with the uretidione ring takes place at lowtemperature, generally from approximately 80 to 100° C., instead of thehigh temperatures described above.

[0025] This property can be taken advantage of in a particularlyadvantageous way in the opening of uretidione rings originating from thecondensation of isocyanate monomers, that is to say of monomers in whichthe NCO functional group is carried by a carbon atom which is stericallyhindered, for example, IPDI dimers, the opening of which is moredifficult than for the true dimers formed by cyclodimerization of weaklyhindered isocyanate monomers, such as HDI.

[0026] A subject matter of the invention is the use of a compoundcomprising at least one nitrogenous heterocyclic group having at leastfive atoms in the ring, at least two of them being nitrogen atoms, forpromoting the reaction of closing uretidione rings or of openinguretidione rings and their reaction with an isocyanate compound or anucleophilic compound comprising a mobile hydrogen atom, with theproviso that, when the nitrogenous heterocyclic group is imidazole, theopening/closing reaction is not the reaction of closing isocyanatecompounds to uretidione rings in the presence of a quaternary ammoniumsalt.

[0027] The nitrogenous cyclic compound advantageously has 5 members andis advantageously selected preferably from imidazole, triazole,tetrazole and their derivatives comprising one or more substituents, inparticular from 1 to 4 substituents, according to the nature of thering.

[0028] The substituents can, independently of one another, be selectedfrom the —R, —OR, —SR, —NRR″, —COR, —CONRR′, —NRCOR′ and —NRCOOR′groups, R and R′, which are identical or different, being selected froma hydrogen atom, a C₁-C₄ alkyl, C₃-C₈ cycloalkyl or C₅-C₁₀ aryl groupand a heterocycle comprising from 2 to 10 carbon atoms and from 1 to 4identical or different heteroatoms selected from O, S and N and the —NR″group, R″ being a C₁-C₄ alkyl or C₃-C₈ cycloalkyl group, the alkyl,cycloalkyl, aryl or heteroaryl groups optionally being substituted byone or more groups selected from OH, COOH, NH₂, SH, alkoxy oralkoxycarbonyl.

[0029] The nitrogenous heterocyclic compound can also be an isocyanatemasked by a masking agent corresponding to the definition of thenitrogenous heterocyclic compounds given above, in other words aprecursor of a nitrogenous heterocyclic compound as defined above.

[0030] Preference is given to the compounds having an imidazole nucleusunsubstituted on the nitrogen atom or having an imidazole nucleuscarrying an N-alkyl or N-aryl substituent having from 1 to 20 carbonatoms, preferably N-methyl.

[0031] According to a first embodiment of the invention, the nitrogenousheterocyclic compound is used to promote the reaction of closing auretidione ring, from starting isocyanate monomers, the latter being inexcess with respect to the nitrogenous heterocyclic compounds.

[0032] According to a second embodiment of the invention, thenitrogenous heterocyclic compound is used to promote the reaction ofopening a uretidione ring in the presence of an anionic compoundresulting in particular from a strong base, said base being inparticular a catalyst for the cyclocondensation of isocyanates.

[0033] A large number of cyclocondensation catalysts, in particularcyclotrimerization catalysts, are anionic compounds within the meaningof the present invention.

[0034] The anionic compound can comprise in particular an alkoxide,hydroxide, fluoride, acetate, carbonate, hydrogencarbonate, carboxylateor a silazane salt of inorganic or organic cations.

[0035] Mention may be made, among inorganic cations, of alkali metals,alkaline earth metals, transition metals and rare earth metals.

[0036] Preference is given, among organic salts, to “oniums” or“iniums”. The oniums are selected from the group of the cations formedby the elements from Groups Vb and VIb (as defined in the Periodic Tableof the Elements published in the Supplement to the “Bulletin de laSociété Chimique de France” in January 1966) with 4 (case of Group Vb)or 3 (case of Group VIb) hydrocarbon chains.

[0037] Advantageously, the organic salt of the invention is, in thiscase, a phosphonium, sulfonium, ammonium, oxonium or diazonium.

[0038] The “iniums”, to which body the pyridiniums belong, derive fromthe oniums by the replacement of two substitutents by a doubly bondedsubstituent.

[0039] A first type of trimerization catalyst particularly suited to theinvention when it is used in combination with a nitrogenous cycliccompound as described above is composed of rare earth metal alkoxides.Reference will be made, for the definition of the rare earth metalelements, to the table on page B-208 of “Handbook of Chemistry andPhysics”, Editor Robert C. Weast, 67th edition).

[0040] These comprise the following elements: scandium yttrium,lanthanum and the lanthanides (cerium, praseodymium, neodymium,samarium, europium, gadolinium, terbium, ytterbium and lutetium).

[0041] According to the invention, it is possible to add a compoundcomprising a rare earth metal alkoxide functional group or a mixture ofcompounds. The rare earth metal alkoxide functional group can consist ofany functional group obtained by substitution of an alcoholic OH groupby a rare earth metal.

[0042] Mention may in particular be made of propoxides, especiallyisopropoxides, in particular the isopropoxide of the following rareearth metal elements: Y, Sm, Yb and La.

[0043] The following are also satisfactorily suitable: methoxides,ethoxides and butoxides, and also alkoxides of poly(alkylene glycol),preferably at least one of the alcohol functional groups of which at thechain end is substituted by an ether or ester functional group or thelike.

[0044] A second type of trimerization catalyst is composed of the alkalimetal, alkaline earth metal, tin or zinc salts, or salts of other metalsof carboxylic acids, such as acetic acid, propionic acid, octanoic acidor benzoic acid.

[0045] A third type of catalyst is composed of the alkali metal,alkaline earth metal, tin or zinc salts of alkoxides or phenoxides.

[0046] A fourth type of catalyst is formed by quaternary ammoniumhydroxides, carbonates, hydrogencarbonates or carboxylates.

[0047] A fifth type of catalyst is composed of the silazane salts or thesilanolates of inorganic or organic cations. These are in particular thecompounds of formula (1) or (2):

[0048] in which the symbols:

[0049] R₁, R₂, R₃, R₄, R₅ and R₆, which are identical or different,represent an aliphatic, cycloaliphatic, which is saturated or unsatured,aryl, aralkyl or alkylaryl monovalent group of hydrocarbon nature,optionally substituted by halogen atoms or CN or ester groups, or

[0050] in the formula (1), one of R₁, R₂, R₃, R₄, R₅ and R₆ represents aunit of formula:

[0051] A being an alkylene group having from 1 to 30 carbon atoms,advantageously from 2 to 20 carbon atoms, preferably (CH₂)_(n′) with n′between 1 and 6, advantageously from 2 to 6,

[0052] and R′₁ to R′₅, which are identical or different, representing analiphatic, cycloalphatic, which is saturated or unsaturated, aryl,aralkyl or alkylaryl monovalent group of hydrocarbon nature, optionallysubstituted by halogen atoms or CN or ester groups, and

[0053] n is an integer between 1 and 50, or

[0054] two from R₁, R₂ and R₃, on the one hand, and/or R4, R₅ and R₆, onthe other hand, together form a divalent hydrocarbon group, and/or

[0055] at least one group selected from R₁, R₂ and R₃ forms, with atleast one group chosen from R4, R₅ and R₆, a divalent hydrocarbonaceousgroup.

[0056] Advantageously, R₁ to R₆ and R′₁ to R′₅, which are identical ordifferent, represent:

[0057] an alkyl, alkenyl, haloalkyl or haloalkenyl group having from 1to 20, preferably from 1 to 6, carbon atoms and optionally comprisingchlorine and/or fluorine atoms,

[0058] a cycloalkyl, cycloalkenyl, halocycloalkyl or halocycloalkenylgroup having from 3 to 30, preferably 3 to 10, carbon atoms andcomprising chlorine and/or fluorine atoms,

[0059] an aryl, alkylaryl or haloaryl group having from 6 to 30,preferably 6 to 10, carbon atoms and comprising chlorine and/or fluorineatoms,

[0060] a cyanoalkyl group having from 1 to 6 carbon atoms,

[0061] or two groups from R₁, R₂ and R₃ or R₃, R₄ and R₅ together form adivalent radical comprising from 2 to 5 carbon atoms,

[0062] or two from R₁, R₂ and R₃, on the one hand, and/or R₄, R₅ and R₆,on the other hand, together form a divalent hydrocarbon group, or

[0063] at least one group selected from R₁, R₂ and R₃ forms, with atleast one group selected from R₄, R₅ and R₆, a divalent hydrocarbongroup comprising from 2 to 5 carbon atoms.

[0064] Particularly preferred groups R₁ to R₆ and R′₁ to R′₅ areselected from methyl, ethyl, propyl, if appropriate linear or branched,vinyl and phenyl, which can optionally be chlorinated and/orfluorinated.

[0065] When the groups R₁ to R₆ and R′₁ to R′₅ are chlorinated and/orfluorinated, the number of halogen atoms varies from 1 to all theavailable valencies.

[0066] Mention may most particularly be made of the salts of thefollowing silazane compounds:

[0067] hexamethyldisilazane

[0068] 1,3-diethyl-1,1,3,3-tetramethyidisilazane

[0069] 1,3-divinyl-1,1,3,3-tetramethyidisilazane

[0070] hexaethyidisilazane, and

[0071] 1,3-diphenyl-1,1,3,3-tetramethyldisilazane.

[0072] Mention may also be made of the following silanolates:

[0073] trimethylsilanolate,

[0074] triethylsilanolate,

[0075] ethyldimethylsilanolate,

[0076] vinyidimethylsilanolate.

[0077] The salt of the compound of formulae (1) and (2) can be amonovalent or multivalent inorganic salt or a mixture of these salts.The preferred inorganic salts are those of K, Li, Na and Mg.

[0078] The salt of the compound of formulae (1) and (2) can also be amonovalent or multivalent organic salt or a mixture of these salts. Thepreferred organic salts are the stable “oniums” or “iniums”.

[0079] In the case of multivalent cations, the salt according to theinvention can comprise at least one ligand of formula (1) or (2) aboveand optionally one or more different ligands. It is generally preferablefor all the ligands to be compounds of formula (1) or (2).

[0080] The number of ligands depends on the valency of the inorganic ororganic cation and on the number of nitrogen atoms in the compound offormula (1).

[0081] When the nucleophilic compound or the solvent is an alcohol, theuse of a catalyst of silazane salt type is avoided.

[0082] It is also possible to use, as catalyst, an anionic compoundhaving a nitrogenous group of the type described above. Mention may inparticular be made of histidine in its metal carboxylate form, whichwill act both via its imidazole heterocycle, to bond to the NCOfunctional group, and the COO⁻ functional group of the amino acid group,to catalyze the cyclotrimerization of the isocyanate monomers.

[0083] A nitrogenous cyclic compound as defined above makes it possible,when it is added to a polycondensation catalyst, in particular acatalyst for the (cyclo)trimerization of isocyanates, of anionic type ina nitrogenous cyclic compound/anionic catalyst molar ratio of between0.1 and 10, in particular between 0.2 and 5, preferably 0.3 and 2.5, toobtain a reaction product comprising true polyisocyanate dimers and truepolyisocyanate trimers in a true polyisocyanate dimers/truepolyisocyanate trimers ratio of greater than 0.5, in particular ofgreater than 0.6, preferably of greater than 0.75, indeed even ofgreater than 1.

[0084] Another subject matter of the invention is a process of thepreparation of a polyisocyanate composition comprising polyisocyanatetrimers, in particular true polyisocyanate trimers, and polyisocyanatedimers, in particular true polyisocyanate dimers, in which the truepolyisocyanate dimers/true polyisocynate trimers molar ratio is greaterthan 0.5, in particular greater than 0.6, preferably greater than 0.75,indeed even greater than 1, in which isocyanate monomers arepolycondensed in the presence of a cyclotrimerization catalyst ofanionic type and of a nitrogenous compound composed of a five-memberedheterocyclic compound having at least two nitrogen atoms, thenitrogenous cyclic compound/anionic catalyst molar ratio being between0.1 and 10, advantageously between 0.2 and 5, preferably between 0.3 and2.5.

[0085] In the present invention, the term “true dimers” denotes thecompounds obtained by condensation of two molecules of startingisocyanate monomers comprising a single uretidione ring.

[0086] The term “true trimers” denotes the compounds obtained bycondensation of three molecules of starting isocyanate monomerscomprising a single uretidione ring.

[0087] The term “heavy compounds” denotes the compounds obtained bycondensation of more than three molecules of isocyanate monomers, inparticular “bis-trimers”, “bis-dimers”, “tris-trimers” and“dimers-trimers”.

[0088] Bis-trimers are polyisocyanate molecules comprising twoisocyanurate rings, in which the link between the two isocyanurate ringsis provided by a monomer unit, namely that two monomer units areinvolved in each of the isocyanurate rings.

[0089] Bis-dimers are polyisocyanate molecules comprising two uretidionerings, in which the link between the two uretidione rings is provided bya monomer unit, namely that two monomers units are involved in each ofthe uretidione rings.

[0090] Tris-trimers are higher homologs of the bis-trimers comprisingthree isocyanurate rings.

[0091] In the case where the monomers are diisocyanates, tris-trimersare obtained by polycondensation of seven monomer chains and comprisethree isocyanurate rings, two consecutive isocyanurate rings beingconnected in pairs by a monomer unit.

[0092] Dimers-trimers are higher homologs of the above compoundscomprising an isocyanurate functional group and a monouretidionefunctional group.

[0093] The process according to the invention can be used for thecyclocondensation of all types of isocyanates or mixtures of isocyanatesas defined above, whether aliphatic, cycloaliphatic or aromatic,including prepolymers having end isocyanate groups, in particular thosedisclosed in U.S. Pat. No. 5,115,071, the content of which isincorporated by reference in the present application. It can also beused for the trimerization of isocyanates in the presence of variousdiols, triols and other polyols with molecular weights lying within awide range, including polyols and aminopolyols, comprising polyether andpolyester groups, employed in the production of polyurethane andpolyisocyanurate resins. However, diisocyanates are preferred.

[0094] The diisocyanates for which the invention is advantageous arethose where the nitrogen atom is bonded to a carbon of sp³ hybridizationand more particularly (cyclo)aliphatic diisocyanates. Mention may inparticular be made of polymethylene diisocyanates, namely the compoundshaving at least two isocyanate functional groups comprising a (CH₂)_(π)sequence where π represents an integer from 2 to 10, advantageously from4 to 8. When there are several sequences, the latter can be the same, ordifferent. In addition, it is desirable for at least one, preferablyall, these sequences to be free to rotate and therefore exocyclic.

[0095] The preferred examples of polymethylene diisocyanates are TMDI(tetramethylene diisocyanate), HDI [hexamethylene diisocyanate,OCN—(CH₂)₆—NCO] and MPDI (2-methylpentane diisocyanate) and the 3,3,5-or 3,5,5-trimethylhexamethylene diisocyanates.

[0096] In the case of a mixture obtained from several (generally two)types of monomers, it is preferable for that or those of the monomerswhich corresponds to the above conditions, and in particular to thecondition with regard to the presence of polymethylene (CH₂), sequences,to represent at least one third, advantageously a half, preferably twothirds, of the masked isocyanate functional groups.

[0097] Isocyanate monomers which are particularly well suited arecycloaliphatic monomers, that is to say those where the backbonecomprises an aliphatic ring.

[0098] These monomers are advantageously such that at least one,advantageously both, isocyanate functional groups is distant from theclosest ring by at the most one carbon, and is preferably connecteddirectly to it. In addition, these cycloaliphatic monomersadvantageously exhibit at least one, preferably two, isocyanatefunctional groups selected from secondary, tertiary or neopentylisocyanate functional groups.

[0099] The best results are obtained when the conformational freedom ofthe cycloaliphatic monomer is low. Mention may be made, as monomerscapable of giving good results, by way of example, of the followingmonomers:

[0100] the compounds corresponding to the hydrogenation of the aromaticnucleus or nuclei carrying isocyanate functional groups of aromaticisocyanate monomers and in particular of TDI (toluene diisocyanate) anddiisocyanatobiphenyls.

[0101] The following compounds are particularly preferred:

[0102] the various BIC [bis(isocyanatomethylcyclohexane)] compounds; andin particular

[0103] norbornane diisocyanate, often known by its abbreviation NBDI;

[0104] isophorone diisocyanate or IPDI or3-isocyanatomethyl-3,5,5-trimethylcyclohexyl isocyanate;

[0105] H₁₂MDI [1,1-methylenebis(4,4-isocyanatocyclohexane)].

[0106] Arylenedialkylene diisocyanates, such as OCN-CH₂-Ø-CH₂-NCO, arealso suitable for the process of the invention.

[0107] When the catalyst is a rare earth metal alkoxide, the nitrogenouscyclic compound/rare earth metal alkoxide molar ratio advantageouslyvaries between 0.1 and 10, preferably between 0.2 and 5.

[0108] The reaction temperature is the temperature commonly employed forthe catalytic trimerization and depends on the type of catalyst.

[0109] When the catalyst is a rare earth metal alkoxide, the reactiontemperature is generally between 20° C., advantageously 50° C., and 200°C., advantageously 150° C.

[0110] When the catalyst is a silazane salt, the reaction temperature isgenerally between 20° C., advantageously 40° C., and 200° C.,advantageously 150° C.

[0111] It is generally preferable to add the catalyst and thenitrogenous cyclic compound simultaneously in a solvent solution to thereaction medium.

[0112] Mention may be made, as solvents, of substituted aromatichydrocarbons, such as Solvesso®, toluene or xylene, or esters (n-butylacetate) or ethers (propylene glycol methyl ether).

[0113] When the catalyst is a rare earth metal alkoxide, it is generallypreferable to add the latter at the same time as the nitrogenous cycliccompound, in particular imidazole or N-methylimidazole, in solution inan alcohol ether, for example methoxyethanol.

[0114] The reaction is stopped at the desired degree of conversion ofthe NCO functional groups. This is generally between 5 and 100%,advantageously between 10 and 80%.

[0115] Another subject matter of the invention is the use of anitrogenous heterocyclic compound as defined above in promoting theopening of a uretidione ring and its reaction with a nucleophiliccompound.

[0116] The nucloephilic compound is advantageously a compound having atleast one functional group having a mobile hydrogen atom, the functionalgroup reacting with the isocyanate functional group, such as alcohols,phenols, amines, thiols, acids, amides, carbamates or ureas, orcompounds which release a functional group comprising mobile hydrogenduring the reaction, in other words the precursors of the compoundslisted above.

[0117] The nucleophilic compound is advantageously selected from amines,alcohols and thiols, preferably primary or secondary alcohols. Use mayalso be made of polyols, polyesters, polyethers, polyacrylics,polyurethanes, and the like.

[0118] The invention is also particularly advantageous for compositionsfor polyurethane powder paints. The polyol compounds are in this casepowder compounds. For compositions for polyurethane powder paints, useis made in particular of IPDI or HDI dimers or their derivatives, orcompositions for powder paints comprising uretidione functional groupsresulting from the condensation of aliphatic or cycloaliphaticisocyanates.

[0119] The advantage of using a heterocyclic compound within the meaningof the invention makes it possible to lower the thermal threshold of thecrosslinking, which is generally between 80 and 150° C. in the presenceof the heterocyclic compound, whereas, in the absence of heterocycliccompound, the crosslinking temperatures are greater than 180° C.,generally between 200 and 220° C. The compositions for powder paints aregenerally stable on storage at a temperature of greater than 0° C.,preferably of greater than 20° C. The choice will therefore be made ofpolyols with a glass transition temperature (Tg) appropriate for thecrosslinking temperature. The Tg depends on the base units of thepolymer and thus on the final structure of the polymer. It is generallybetween −20° C. and 150° C., preferably between 0 and 100° C. andadvantagouesly between 20 and 80° C.

[0120] In the case of polyurethane powder compositions, the heterocycliccompound can be incorporated at various stages in the manufacture of thepowder paint, either at the stage of the synthesis of the dimercompound, or in the polyol, or during the manufacture of the powderpaint in combination with the various constituents of the paint, forexample during extrusion.

[0121] The operating conditions for the preparation of this powder willthus be optimized so that there is not an excessively great reactionbetween the dimer and the compounds comprising mobile hydrogen.

[0122] To do this, the extrusion conditions, namely the conditions forextrusion of the polyurethane powder paint, will in particular beoptimized, the extrusion temperature generally being approximately 100°C. with an extrusion time of less than 30 minutes.

[0123] The nucleophilic functional group/uretidione ratio is between 10and 0.05, preferably between 5 and 0.1, advantageously between 3 and0.25, it being possible for this ratio to be obtained at any stage ofthe crosslinking reaction. In the case where the ratio is small, dimerfunctional groups are retained and can react subsequently with othersubsequent nucleophilic functional groups. In the case where the ratiois higher, the nucleophilic functional groups are retained and can reactwith other functional groups, such as free isocyanate, maskedisocyanate, anhydride or oxirane functional groups, and the like.

[0124] In the case of powder paints, it is preferable for theheterocyclic compounds to be solids, that is to say for them to have amelting point of greater than 25° C., preferably of greater than 50° C.Preference will therefore be given to heterocyclic compounds, preferablysubstituted heterocyclic compounds, having an aliphatic chain with anumber of carbon atoms of between 1 and 10.

[0125] Use may also be made of heterocyclic compounds according to theinvention in solution with polyols and uretidione polyisocyanatecompounds. In this case, the same solvent will be selected as that usedfor the final formulations, preferably an ester, ether, substitutedaromatic hydrocarbon or possibly water for the compositions of waterpaint type.

[0126] It is not necessary for the nucleophilic compound participatingin the opening of the uretidione ring by the nitrogenous heterocycliccompound to be an ionic compound. However, the presence of such acompound is not harmful to the reaction of opening the ring and thus theapplication of the final coating.

[0127] The following examples illustrate the invention. Unless otherwiseindicated, percentages are expressed by weight. The trimerizationcatalysvimidazole ratios are molar ratios.

EXAMPLE 1

[0128] Polycondensation of IPDI in the Presence of Lanthanumtris(2-methoxy-ethylene glycolate) and of imidazole

[0129] Preparation of the Catalyst Solution:

[0130] The catalyst solution is prepared in a first step:

[0131] 1.87 g (0.0275 mol) of imidazole are introduced into 100 mL of a10 weight % solution of lanthanum tris(2-methoxy-ethylene glycolate) in2-methoxyethanol (density 1.01). The imidazole/lanthanumtris(2-methoxy-ethylene glycolate) molar ratio is equal to 1.

[0132] Reaction

[0133] 20 g of isophorone diisocyanate (IPDI), i.e. 0.09 mol, i.e. 0.18mol of NCO, are added at ambient temperature under a stream of nitrogento a 50 mL 3-necked reactor. The catalytic solution (1 g, i.e. 2.75×10⁻⁴mol of imidazole and 2.75×10⁻⁴ mol of lanthanum tris(2-methoxy-ethyleneglycolate)) is added to the reaction medium. The amounts of lanthanumalkoxide and of imidazole are respectively equal to 100 mg and 19 mg,i.e. a metal/NCO ratio of 1.5×10⁻³. The temperature of the reactionmedium is brought to 60° C. and the reaction is left stirring for 5hours and is then blocked by addition of para-toluenesulfonic acid (200mg). The degree of conversion of the IPDI is 54.7%.

[0134] The analysis of the reaction medium before removal of the IPDImonomer is presented in the table below: Percentages by Product weightIPDI 55.3 Carbamate of IPDI and of 2-methoxyethanol Allophanate of IPDIand of 2-methoxyethanol 8.8 IPDI dimmer 13.8 True IPDI trimer 13.2 IPDIbis-trimer 6.8 Heavy compounds, including tris-trimers 2.1 Truetrimer/sum of the trimers ratio 0.625 True trimer/sum of the true dimersand trimers ratio 1 True dimer/true trimer ratio 1.04

[0135] The presence is recorded of allophanate and dimer functionalgroups under the unresolved peaks of the bis-trimers and heavycompounds.

EXAMPLE 2

[0136] Polycondensation of IPDI in the Presence of Yttriumtris(2-methoxy-ethylene Glycolate) and of Imidazole

[0137] The operation is carried out as for example 1, the lanthanumalkoxide being replaced by that of yttrium.

[0138] 20 g of isophorone diisocyanate (IPDI), i.e. 0.09 mol, i.e. 0.18mol of NCO, are added at ambient temperature under a stream of nitrogento a 50 mL 3-necked reactor. The catalytic solution is added to thereaction medium. The amounts of yttrium alkoxide and of imidazole arerespectively equal to 150 mg and 32 mg, i.e. a metal/NCO ratio of2.6×10⁻³. The temperature of the reaction medium is brought to 60° C.and the reaction is left stirring for 5 hours and is then blocked byaddition of para-toluenesulfonic acid (200 mg). The degree of conversionof the IPDI is 41%.

[0139] The analysis of the reaction medium before removal of the IPDImonomer is presented in the table below: Percentages by Product weightIPDI 59 Carbamate of IPDI and of 2-methoxyethanol 1.6 Allophanate ofIPDI and of 2-methoxyethanol 9.6 IPDI dimmer 15.2 True IPDI trimer 8.4IPDI bis-trimer 3.8 Heavy compounds, including tris-trimers 0.8 Truetrimer/sum of the trimers ratio 0.65 True trimer/sum of the true dimersand trimers ratio 0.3 True dimer/true trimer ratio 1.81

[0140] The presence is recorded of allophanate and dimer functionalgroups under the unresolved peaks of the bis-trimers and heavycompounds.

EXAMPLE 3

[0141] Polycondensation of IPDI in the Presence of Yttriumtris(isopropoxide) and of Imidazole

[0142] 20 g of isophorone diisocyanate (IPDI), i.e. 0.09 mol, i.e. 0.18mol of NCO, are added at ambient temperature under a stream of nitrogento a 50 mL 3-necked reactor. 200 mg of yttrium tris(isopropoxide)(7.5×10 ⁻⁴ mol) and 51 mg of imidazole are added, i.e. a metal/NCO ratioof 4×10⁻³. The temperature of the reaction medium is brought to 60° C.and the reaction is left stirring for 5 hours and is then blocked byaddition of para-toluenesulfonic acid (150 mg). The NCO assay is 0.552and the degree of conversion of the IPDI is 77.3%.

[0143] The analysis of the reaction medium before removal of the IPDImonomer is presented in the table below: Percentages Product by weightIPDI 23.6 Carbamate of IPDI and of isopropyl Allophanate of IPDI and ofisopropyl 3.5 IPDI dimmer 20.9 True IPDI trimer 22 Bis-trimer andtrimer-dimer of IPDI and trimer-allophanate 10.3 Heavy compounds,including tris-trimers 0.8 True trimer to sum of the trimers ratio 0.66True trimer to sum of the true dimer and true trimer ratio 0.41 Truedimer/true trimer ratio 0.95

[0144] The presence is recorded of allophanate and dimer functionalgroups under the unresolved peaks of the bis-trimers and heavycompounds.

EXAMPLE 4

[0145] Polycondensation of IPDI in the Presence of Neodymiumtris(isopropoxide)

[0146] The operation is carried out as for example 3, the yttriumalkoxide being replaced by that of neodymium.

[0147] 20 g of isophorone diisocyanate (IPDI), i.e. 0.09 mol, i.e. 0.18mol of NCO, are added at ambient temperature under a stream of nitrogento a 50 mL 3-necked reactor. 1% by weight of neodymiumtris(isopropoxide) with respect to the IPDI, i.e. 200 mg (i.e. 6.2×104mol, i.e. a metal/NCO ratio of 3.5×10⁻³) and 42 mg of imidazole areadded to the reaction medium. The temperature of the reaction medium isbrought to 60° C. and the reaction is left stirring for 5 hours. Thereaction is halted by addition of 200 mg of para-toluenesulfonic acid.

[0148] The analysis of the reaction medium before distillation of theIPDI monomer by chromatography gives the following composition:Percentages by Product weight IPDI 39.4 Carbamate of IPDI and ofisopropyl 0 Allophanate of IPDI and of isopropyl 1.2 IPDI dimmer 31.4IPDI bis-dimer 4.6 True IPDI trimer 13 IPDI bis-trimer 4.8 Heavycompounds, including tris-trimers 4.2 True trimer to sum of the trimersratio 0.59 True trimer to sum of the true dimer and true trimer ratio0.3 True dimer/true trimer ratio 2.4

[0149] The presence is recorded of allophanate functional groups underthe unresolved peaks of the bis-trimers and heavy compounds.

EXAMPLE 5

[0150] Polycondensation of IPDI in the Presence of Yttriumtris(isopropoxide) and of imidazole

[0151] 20 g of isophorone diisocyanate (IPDI), i.e. 0.09 mol, i.e. 0.18mol of NCO, are added at ambient temperature under a stream of nitrogento a 50 mL 3-necked reactor. 200 mg of yttrium tris(isopropoxide)(7.5×10⁻⁴ mol) and 51 mg of imidazole are added, i.e. a metal/NCO ratioof 4×10⁻³. The temperature of the reaction medium is brought to 60° C.and the reaction is left stirring for 5 hours and is then blocked byaddition of para-toluenesulfonic acid (150 mg). The NCO assay is 0.552and the degree of conversion of the IPDI is 77.3%.

[0152] The analysis of the reaction medium before removal of the IPDImonomer is presented in the table below: Percentages Product by weightIPDI 23.6 Carbamate of IPDI and of isopropyl Allophanate of IPDI and ofisopropyl 3.5 IPDI dimer 20.9 True IPDI trimer 22 Bis-trimer andtrimer-dimer of IPDI and trimer-allophanate 10.3 Heavy compounds,including tris-trimer 0.8 True trimer to sum of the trimers ratio 0.66True trimer to sum of the true dimer and true trimer ratio 0.41 Truedimer/true trimer ratio 0.95

EXAMPLE 6

[0153] Polycondensation of IPDI in the Presence of Yttriumtris(isopropoxide) and of N-methylimidazole

[0154] 20 g of isophorone diisocyanate (IPDI), i.e. 0.09 mol, i.e. 0.18mol of NCO, are added at ambient temperature under a stream of nitrogento a 50 mL 3-necked reactor. 200 mg of yttrium tri(isopropoxide)(7.5×10⁻⁴ mol) and 51 mg of N-methylimidazole are added, i.e. ametal/NCO ratio of 4×10⁻³. The temperature of the reaction medium isbrought to 60° C. and the reaction is left stirring for 5 hours and isthen blocked by addition of para-toluenesulfonic acid (150 mg). Thepresence of dimer and trimer bands is observed.

[0155] The analysis of the reaction medium before removal of the IPDImonomer is presented in the table below: Percentages Product by weightIPDI 50 Carbamate of IPDI and of isopropyl Allophanate of IPDI and ofisopropyl 3 IPDI dimmer 5 True IPDI trimer 23 Bis-trimer andtrimer-dimer of IPDI and trimer-allophanate 12 Heavy compounds,including tris-trimers 7 True trimer to sum of the trimers ratio 0.55True trimer to sum of the true dimer and true trimer ratio 0.49 Truedimer/true trimer ratio 0.2

[0156] The presence is recorded of allophanate and dimer functionalgroups under the unresolved peaks of the bis-trimers and heavycompounds.

COMPARATIVE EXAMPLE 1

[0157] The operation is carried out as for example 1, except that amethoxybutanol solution comprising 5% by weight of lanthanumtris(2-methoxy-ethylene glycolate) is added.

COMPARATIVE EXAMPLE 2

[0158] The operation is carried out as for example 2, except that amethoxyethylethoxide solution comprising 5% of yttriumtris(2-methoxy-ethylene glycolate) is added.

COMPARATIVE EXAMPLE 3

[0159] The operation is carried out as for example 3, except that asolution comprising 200 mg of yttrium tris(isopropoxide) is added.

COMPARATIVE EXAMPLE 4 (CMI 129902)

[0160] The operation is carried out as for example 4, except that asolution comprising 200 mg of neodymium tris(isopropoxide) is added. Theresults are reported in the table below: TABLE Ex.2 5% 50/50 Y Ex. 1meth- Ex. 3 Ex. 4 5% 50/50 oxyethoxide Comp. Ex. 1 Comp. Ex. 2 50/5050/50 Comp. Product/Component alkoxide/ alkoxide/ 5% 5% Y(iPrO)₃ Comp.Ex. 3 Nd(iPrO)₃/ Ex. 4 Catalyst imidazole imidazole La alkoxide Yalkoxide imidazole Y(iPrO)₃ imidazole Nd(iPrO)₃ IPDI 55.3 59.0 25.5 61.523.6 7.9 39.4 16.5 True dimer 13.8 15.2 20.9 31.4 Bis-dimer — 4.6 IPDIcarbamates — 1.6 0.5 1.6 True trimer 13.2 8.4 27.0 11.6 22 32.1 13 40.2Bis-trimers + (trimer-dimers) 6.8 3.8 20.4 12.0 9.1 17.3 4.8 21.3 Heavycompounds 2.1 0.8 19.9 5.4 7.5 35.3 3.2 6.4 Trimer-allophanate 1.2 2.61.2 0.8 Allophanate of IPDI and 8.8 9.6 6.7 9.5 3.5 3.2 1.2 1.2originating from the alkoxide True trimers/true trimers + 1 0.51 1 0.3 1true dimers ratio by weight True dimers/true trimers ratio 1.04 1.810.95 2.4 by weight

1. Use of a compound comprising at least one nitrogenous heterocyclicgroup having at least five ring members, at least two of them beingnitrogen atoms, for promoting the reaction of closing uretidione ringsor of opening uretidione rings and their reaction with a nucleophiliccompound comprising a mobile hydrogen atom, with the proviso that, whenthe nitrogenous heterocyclic group is imidazole, the opening/closingreaction is not the reaction of closing isocyanate compounds touretidione rings in the presence of a quaternary ammonium salt.
 2. Theuse as claimed in claim 1, characterized in that the nitrogenousheterocyclic compound is employed to promote the cyclodimerization ofisocyanate compounds in the presence of an anionic compound, theisocyanate compounds being in excess with respect to the nitrogenousheterocyclic compounds, with the proviso that the cyclodimerization isnot carried out in the presence of quaternary ammonium when thenitrogenous heterocyclic compound is imidazole.
 3. The use as claimed inclaim 1, characterized in that the nitrogenous heterocyclic compound isemployed to promote the reaction of opening a uretidione ring in thepresence of a nucleophilic compound.
 4. The use as claimed in claim 3,characterized in that the nucleophilic compound is the reaction productof a base with an isocyanate group.
 5. The use as claimed in claim 3,characterized in that the nucleophilic compound is a compound having afunctional group having a mobile hydrogen atom, the functional groupreacting with the isocyanate functional group.
 6. The use as claimed inclaim 4, characterized in that said nucleophilic compound is selectedfrom amines, alcohols and thiols.
 7. The use as claimed in claim 1,characterized in that said nitrogenous cyclic compound is selected fromimidazole, triazole, tetrazole and their derivatives comprising one ormore substituents.
 8. The use as claimed in claim 7, characterized inthat the five-membered nitrogenous heterocyclic compound is imidazole orone of its derivatives comprising one or more substituents.
 9. A processfor the preparation of a polyisocyanate composition comprisingpolyisocyanate trimers, in particular true polyisocyanate trimers, andpolyisocyanate dimers, in particular true polyisocyanate dimers, inwhich the true polyisocyanate dimers/true polyisocyanate trimers molarratio is greater than 0.5, in particular greater than 0.6, preferablygreater than 0.75, in which isocyanate monomers are polycondensed in thepresence of a cyclotrimerization catalyst of anionic type and of anitrogenous compound composed of a five-membered heterocyclic compoundhaving at least two nitrogen atoms in a nitrogenous cycliccompound/anionic catalyst molar ratio of between 0.1 and 10,advantageously between 0.2 and
 8. 10. The use as claimed in claim 9,characterized in that the (cyclo)trimerization catalyst is selected fromthe group consisting of alkoxides, hydroxides, fluorides, acetates,carbonates, hydrogencarbonates, carboxylates and silazane salts ofalkali metals, alkaline earth metals, transition metals and rare earthmetals and of cations of onium or inium type.
 11. The process as claimedin claim 10, characterized in that the (cyclo)trimerization catalyst isa rare earth metal alkoxide.
 12. The use as claimed in claim 8,characterized in that the (cyclo)trimerization catalyst is a quaternaryammonium hydroxide, hydrogencarbonate or carboxylate.
 13. The use asclaimed in claim 8, characterized in that the (cyclo)trimerizationcatalyst is a silazane salt of alkali metals, alkaline earth metals,transition metals and rare earth metals and cations of onium or iniumtype.
 14. A compound of formula (II):

R being the residue of an isocyanate compound after removal of anisocyanate functional group and HET being a nitrogenous heterocycliccompound as defined in claim 1 bonded to the NCO group via a nitrogenatom of the heterocycle.